High strength, high modulus pitch-based carbon fiber

A high strength, high modulus pitch-based carbon fiber comprising a crystalline structure in which the presence of the (112) cross-lattice line and the resolution of the diffraction band into the (100) and (101) defraction lines, which indicate the 3-dimensional order of the crystallite of t he fiber, are not recognized, and in which the orientation angle (.PHI.) of X-ray structural parameter is not greater than 12.degree. and the stack height (Lc) ranges between 80 and 180.ANG., said carbon fiber also having a single-fiber diameter of 5 to 12.mu.m, tensile strength not lower than 3.0 GPa, tensile elastic modulus not smaller than 500 GPa and elongation not smaller than 0.5%, said carbon fiber being prepared by a process comprising the steps of:

• (a) spinning of mesophase molten pitch to obtain a pitch fiber wherein the temperature drop of the pitch is maintained at a level below about 3.degree. C. by using a nozzle which incorporates an insert member having a high heat conductivity.
• (b) infusibilizing said pitch fiber by heating said pitch fiber in an atmosphere of an inert gas from a minimum temperature ranging from about 120.degree. C to about 190.degree. C. to a maximum temperature ranging from about 240.degree. C. to about 350.degree. C. at a heating rate of about 0.005.degree. C./minute to about 0.1.degree. C./minute, while said pitch fiber is under a tension ranging from about 0.0001 gram per filament to about 0.2 gram per filament, and
• (c) carbonizing said infusibilized fiber by heating said infusibilized fiber in an inert gas atmosphere up to a temperature of about 1,000.degree. C. at a rate of about 0.1.degree. C./minute to about 10.degree. C./minute, and thereafter heating said infusibilized fiber to a maximum temperature ranging from about 1,700.degree. C. to about 2,500.degree. C. at a rage of about 10.degree. C./minute to about 500.degree. C./minute.